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Chapter 3 Molecules, Compounds, and Chemical Equations

Chapter 3 Molecules, Compounds, and Chemical Equations. Elements and Compounds. Elements combine together to make an almost unlimited number of compounds The properties of a compound are totally different from its constituent elements. Formation of Water from Its Elements. Chemical Bonds.

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Chapter 3 Molecules, Compounds, and Chemical Equations

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  1. Chapter 3Molecules, Compounds, and Chemical Equations

  2. Elements and Compounds • Elements combine together to make an almost unlimited number of compounds • The properties of a compound are totally different from its constituent elements

  3. Formation of Water from Its Elements

  4. Chemical Bonds • Compounds are made of atoms held together by chemical bonds • attractive forces between each atoms’ protons and the bonding electrons

  5. Two general Bond TypesIonic and Covalent • Ionic bondsresult when electrons have been transferred between a metal and a nonmetal atom, resulting in oppositely charged ions that attract each other • Covalent bondsresult when two atoms share one or more of their electrons • generally found when nonmetal atoms bond together

  6. Formulas Describe Compounds Each element is represented by its letter symbol The number of atoms of each element is written to the right of the element’s symbol as a subscript A compound is a distinct substance composed of atoms from two or more elements the compound is defined by the number and type of each atom compounds can be a neutral molecule or an ion

  7. An element is made up of • Multiple types of atoms • Compounds • A single type of atom

  8. Representing Compounds with Chemical Formulas • Compounds are generally represented with a chemical formula • All chemical formulas tell what elements are in the compound through use of the letter symbol of the element • All formulas and models convey a limited amount of information – none are perfect representations

  9. Types of Formulas: Empirical Formula • A compound’s empirical formulagives the relative number of atoms of each element reduced to the lowest possible denominator • it doesn’t describe the # atoms, the order of attachment, or the shape • formulas of ionic compounds are empirical • Fluorspar (CaCl2) is an ionic compound. There is 1 Ca2+ ion for every 2 Cl− ions in the compound. • molecular compounds can also be written as an empirical formula • e.g. the molecular formula for oxalic acid is C2H2O4 but the empirical formula is CHO2

  10. Types of Formula: Molecular Formula • Amolecular formulagives the actual number of atoms of each element in a molecule • it does not describe the order of attachment, or the shape • The molecular formula C2H2O4. • tells you that there are 2 carbon atoms, 2 hydrogen atoms, and 4 oxygen atoms • Doesn’t tell you how the carbon, oxygen and hydrogen atoms are attached together

  11. Types of Formula: Structural Formula • A structural formulatells what atoms are present and how the atoms in a molecule are attached together. • It uses lines to represent covalent bonds • it does not describe the 3-dimensional shape, but an experienced chemist can make a good guess at it • each line describes the number of electrons shared by the bonded atoms • single line = 2 shared electrons, a single covalent bond • double line = 4 shared electrons, a double covalent bond • triple line = 6 shared electrons, a triple covalent bond

  12. Representing Compounds Molecular Models • Molecular models show the 3-d structure of the molecule plus all the information given by the structural formula • Ball-and-stick models use balls to represent the atoms and sticks to represent the bonds between them • Space-filling models use interconnected spheres to show the electron clouds of atoms connecting together

  13. Structural Formula of Oxalic Acid Space filling Model Ball and Stick Model

  14. The following formulas represent: / C2O4H2 / CO2H • Empirical / Molecular / Structural • Molecular / Empirical / Structural • Structural / Molecular / Empirical • Empirical / Structural / Molecular • Molecular / Structural / Empirical • Structural / Empirical / Molecular

  15. The ionic compound that has two aluminum ions for every three oxide ions arabinose, C5H10O5 pyrimidine ethylene glycol Write the empirical formula for each of the following Al2O3 CH2O C2H2N CH3O

  16. Classification of Elements and Compounds

  17. Classifying Elements • Atomic elements • Single atoms • Most elements are atomic elements • Diatomic elements • 2 atoms (e.g. H2) • Polyatomic elements • more than 2 atoms (e.g. P4, S8, Se8)

  18. 5A 6A 7A N7 O8F9 H1 Cl17 Br35 I53 Molecular Elements • 7 elements occur as diatomic molecules (2 atoms) 1A • shaped like a 7 on the periodic table… • start with element 7, N – group V, go across the table to group VIIA, F, then go down group VIIA to I • Hydrogen stands alone • Other elements occur as polyatomic molecules • P4, S8, Se8

  19. Molecular Elements

  20. Classifying Compounds • Ionic compounds a 3-D array of anions surrounded by cations and vice-versa • Made from combining metals (which form cations) with non-metals (which form anions) • No individual molecular units, only formula units • Can contain polyatomic ions • 2+ atoms attached together by covalent bonds with an overall charge on the entire ion Table salt – contains an array of Na+ ions and Cl- ions

  21. = Alkali metals Li F Mg Na Cl Ca K Br Sr Rb I Ba Cs = Alkali earth metals = Halogens Ions with predictable charges -3 1A 2A 7A 8A +3 3A 4A 5A 6A +1 +2 O N -1 Al S Se Te -2

  22. Compounds that Contain Ions • A neutral compound must have no total charge, therefore the number of cations and anions multiplied by their charges, must balance to get 0 charge • If Na+ is combined with S2−, you will need 2 Na+ ions for every S2− ion to balance the charges, therefore the formula must be Na2S

  23. Classify the Following as Either an Atomic Element, Molecular Element, Molecular Compound, or Ionic Compound atomic element ionic compound molecular element molecular compound molecular compound atomic element Aluminum, Al Aluminum chloride, AlCl3 Chlorine, Cl2 Acetone, C3H6O Carbon monoxide, CO Cobalt, Co

  24. Ex 3.4: Write a formula for ionic compound that forms between calcium and oxygen Ca2+ O2− CaO cations: +2 anions: −2 The charges cancel

  25. Example 3.3: Write the formula of a compound made from aluminum ions and oxide ions Al3+ column 3A • Write the symbol for the metal cation and its charge • Write the symbol for the nonmetal anion and its charge • Charge (without sign) becomes subscript for other ion • Reduce subscripts to smallest whole number ratio • Check that the total charge of the cations cancels the total charge of the anions O2− column 6A Al+3 O2− Al2O3 no change required Al = (2)∙(+3) = +6 O = (3)∙(−2) = −6

  26. Write the formulas for compounds made from the following ions • Potassium ion with a nitride ion K+ with N3− • Calcium ion with a bromide ion Ca2+ with Br1− • Aluminum ion with a sulfide ion Al3+ with S2− K3N CaBr2 Al2S3

  27. Rules for Naming Ionic Compounds • Some compounds have common names that can only be learned by memorization • NaCl = table salt • NaHCO3 = baking soda • Others have a systematic name based on naming the component ions

  28. Naming Binary Ionic Compounds forMetalswith Invariant Charge • First, use the metal’s elemental name for the cation • Next,add the nonmetal anion’s name • assign the proper negative charge based its group number on the Periodic Table • the nonmetal name’s suffix changes to -ide

  29. CsF: A Binary Ionic Compound with a Metalhaving Invariant Charge • 1. Identify cation and anion Cs = Cs+ because it is Group 1A F = F− because it is Group 7A • 2. Name the cation Cs+ = cesium • 3. Name the anion F− = fluoride • 4. Write the cation name first, then the anion name cesium fluoride

  30. Naming Binary Ionic Compounds forMetalswith Variable Charge • Again, use the elemental metal name for the metal cation • Determine the anion’s charge cation’s charge • A (Roman Numeral) follows the metal ion to indicate its charge • Next add the nonmetal anion’s name • the nonmetal name’s suffix changes to -ide

  31. CuF2: A Binary Ionic Compound with a Metalhaving Variable Charge • Identify cation and anion • F = F− because it is Group 7A Cu = Cu2+ to balance the two (−) charges from 2 F− • 2. Name the cation Cu2+ = copper(II) • 3. Name the anion F− = fluoride • 4. Write the cation name first, then the anion name copper(II) fluoride

  32. Name the compound composed of chlorine and potassium: KCl • potassium (I) chloride • chlorine potassiumide • potassium chloride • potassium chlorine

  33. Name the compound composed of magnesium and bromine: MgBr2 • magnesium bromide • magnesium (II) dibromide • bromine magneside • bromine magnesiumide • magnesium dibromine

  34. Name the compound composed of aluminum and sulfur: Al2S3 • trisulfur dialuminide • aluminum (III) trisulfide • sulfur magnesiumide • aluminum sulfuride • aluminum sulfide

  35. Determining the charge on a metal cation having variable charge in a compound composed of gold and sulfur: Au2S3 • Determine the invariant charge on the anion Au2S3: the anion is S = Group 6A, its charge is 2− • Determine the total negative charge 3 S in the formula, the total negative charge is 3 x 2 − = 6− • Set the total positive charge = total negative charge total negative charge = 6−, total positive charge = 6+ • Divide by the number of cations in the formula • with 2 Au in the formula and a total positive charge of 6+, each Au must have a 3+ charge • The compound name is Gold (III) Sulfide

  36. Find the charge on the cation CrO3 Fe3N2 Name the compound each O = 2− 3 O = 6− chromium (VI) oxide  Cr = 6+ Name the compound each N = 3− 2 N = 6− iron (II) nitride 3 Fe = 6+  Fe = 2+

  37. Find the charge on the cation in TiCl4 • -1 • -4 • +1 • +4

  38. Find the charge on the cation • TiCl4 each Cl = 1- 4 Cl = 4−  Ti = 4+ Name the compound titanium(IV) chloride

  39. Name the compound each Br = -1 2 x -1= -2  Pb 2+ • PbBr2 • Fe2S3 lead(II) bromide iron(III) sulfide each S = -2 3 x -2= -6 -6/2 Fe = -3  Fe 3+

  40. To Write the formula for a binary ionic compound containing metal with variable chargemanganese(IV) sulfide 1. Write the symbol for the cation and its charge 2. Write the symbol for the anion and its charge 3. The charge (without the sign) becomes subscript for other ion 4. Reduce subscripts to smallest whole number ratio 5. Check that the total charge of the cations cancels the total charge of the anions Mn4+ S2- Mn4+ S2− Mn2S4 MnS2 Mn = (1)∙(4+) = +4 S = (2)∙(2−) = −4

  41. What are the formulas for compounds made from copper (II) nitride, Cu2+ with N3− • Cu2N3 • Cu3N2 • N3Cu2 • N2Cu3

  42. What are the formulas for compounds made from iron(III) with bromide: Fe3+ with Br- • FeBr3 • Fe3Br • FeBr • Br3Fe • BrFe3

  43. Compounds Containing Polyatomic Anions • Name the cation first, then the polyatomic anion • The name and the charge of the polyatomic ion do not change • If more than one polyatomic ion is present, the polyatomic ion is surrounded by parentheses • a subscript tells how many polyatomic ions there are. NO3- (NO3-)2 (NO3-)3

  44. Periodic Pattern of Polyatomic Ions Elements in the same column form similar polyatomic ions - ate groups

  45. Patterns for Polyatomic Ions -ate ion chlorate = ClO3− • remove 2 oxygen • with same charge • hypochlorite = ClO− add 1 oxygen with same charge perchlorate = ClO4− • remove 1 oxygen • with same charge • chlorite = ClO2−

  46. Some Common Polyatomic Ions If the polyatomic ion has a H in the front, add hydrogen- as a prefix and adjust the overall charge by +1

  47. Example: Naming ionic compounds containing a polyatomic ion - Na2SO4 • 1. Identify the ions 2Na = 2Na+ because in Group 1A SO4 = SO42− a polyatomic ion • 2. Name the cation Na+ = sodium, metal with invariant charge • 3. Name the anion SO42− = sulfate • 4. Write the name of the cation followed by the name of the anion sodium sulfate

  48. Example: Naming ionic compounds containing a polyatomic ion Fe(NO3)3 • 1. Identify the ions NO3 = NO3− a polyatomic ion Fe = Fe3+ to balance the charge of the 3 NO3− • 2. Name the cation Fe3+ = iron(III), a metal with variable charge • 3. Name the anion NO3− = nitrate • 4. Write the name of the cation followed by the name of the anion iron(III) nitrate

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